1. Field of the Invention
This invention relates to a cobalt-based heat-resisting composition used as a spinner wheel material to prepare glassfiber and more particularly, to a cobalt-based heat-resisting alloy having excellent strength, anti-abrasiveness and antioxidative effects at a higher temperature. To establish the chemical composition of an alloy suitable for vacuum melting and casting, Mn and Si are added to the basic alloy composition consisting of Co, Cr, Ni and W, thus controlling a deoxidating effect and fluidity; Nb, Ti, V, Zr, C and Si are used as other additive elements instead of using the conventional high-priced rare earth metals (such as Y), as well as Ta, Hf and B with the allowed scope of impurities enlarged, thereby preventing any casting defects from the generation of bubbles; since cementite crystal phase of both Nb and Cr is evenly distributed within an alloy and more strong web of the three-dimensional network structure, such crystal phase is strongly supported by austenite structure of Co and Ni having tungsten carbide and Zr as a nucleus.
2. Description of the Prior Art
In general, glassfiber is formed, when melted glass is passed by centrifugal force through walls having multiporous holes in a high speed-rotation spinner wheel.
Spinner is generally operated at about 1,100.degree. C. at 2,000 rpm. Since glassfiber comes out from small porous walls in a spinner having a higher rotation speed, high fracture strength at high temperature and high corrosion-resistive property against melting glass should be required.
According to the conventional cobalt-based heat-resisting alloy used for a spinner wheel, the following chemical composition by weight % is generally provided: 30% of Cr, 13% of Ni, 10% of W, 2% of Ta and the balance consisting of Co and other elements such as less than 1% of silicon, less than 0.5% of carbon and Zr, B and Y in a small amount depending on the selected elements.
Now that the conventional alloy failed to fully meet the mechanical strength required for a high-speed rotation spinner wheel, however, demand has been increasing for alternative alloy having more high stress fracture and corrosion-resistive properties. In response to this demand, some alloys were proposed in the U.S. Pat. Nos. 4,620,324 and 4,904,290. In these patents, however, the alloys containing some high-priced metals such as Ta, Y and B cannot be easily purchased in the local market, having been in particular characterized in that Hf is not contained in the currently marketed metals as an impurity. In spite of the fact that such alloys have better anti-abrasiveness property and antioxidative effect compared to the conventional alloy, these patents still impose significant limitations on the continuous manufacture of glassfiber for a prolonged period of time under severe conditions.
To comply with these problems, a cobalt-based heat-resisting alloy was developed by this applicant, as proposed in Korean Examined Patent Publication No. 94-8942. This patent relates to an alloy having strength, deoxidative effect and glass corrosion-resistive property at a higher temperature, and is advantageous in that this alloy is suitable for the prolonged use in the glassfiber-forming spinner wheel, while providing in particular a cobalt-based heat-resisting alloy fabricated by the air-melt casting method.
However, this patent has some problems in that since such alloy is formed by the air-melt casting method, the surface of cast is coarse and any casting defects such as fine bubbles in the alloy structure during solidification may occur due to oxygen infiltrated into the liquid metal during the melting process.
Namely, the alloy liquid (liquid phase) at such temperature range, being subjected to infiltration by excessive amount of oxygen and nitrogen in the air, is present as an instable form of oxide or nitride. When the melting material is poured to a cast, it is not crystallized and bubbles generated during reduction weaken the binding power of an alloy and are responsible for lowering the yielding point at a higher temperature.